我无法登录FTP服务器，因为它提供了+ QFTPOPEN：609,0，其中609错误代码用于超时操作。我遵循了所有步骤
//Step 1: Configure and activate the PDP context.
AT+QICSGP=1,1,“UNINET”,“”,“”,1 //Configure PDP context 1. APN is “UNINET” for
China Unicom.
OK
AT+QIACT=1 //Activate PDP context 1.
OK //Activated successfully.
AT+QIACT? //Query the state of PDP context.
+QIACT: 1,1,1,“10.7.157.1”
OK
AT+QFTPCFG=“contextid”,1 //Configure the PDP context ID as 1. The PDP context
ID must be activated first.
OK
//Step 2: Configure user account and transfer settings.
AT+QFTPCFG=“account”,“test”,“test” //Set user name and password.
OK
AT+QFTPCFG=“filetype”,1 //Set file type as binary.
OK
AT+QFTPCFG=“transmode”,1 //Set transfer mode as passive mode.
OK
AT+QFTPCFG=“rsptimeout”,90 //Set response timeout value.
OK
//Step 3: Login to FTP server.
AT+QFTPOPEN=“2.2.2.250"
OK
+QFTPOPEN: 0,0
但是我无法成功连接。